Digital Fourier transform spread orthogonal frequency division multiplexing to (DFT spread OFDM) method has a low Cubic Metric (CM) and equivalently low Peak to Average Power Ratio (PAPR). Therefore, a power amplifier may be used efficiently. With the merit, DFT spread OFDM method has been adopted as an uplink transmission method of 3rd Generation Partnership Project (3GPP) long term evolution (LTE) system, and it is considered that it will be adopted as an uplink transmission method of 3GPP LTE-Advanced. DFT spread OFDM is also referred to Single Carrier Frequency Division Multiple Access (SC-FDMA) equivalently.
A reference symbol or a pilot signal is transmitted from a data transmission apparatus to a data reception apparatus for a channel estimation, and the like, in the data reception apparatus. In 3GPP LTE, a reference symbol is transmitted using a single OFDM symbol for every slot. This is for preventing the CM and PAPR from increasing when data and a reference symbol are mixed in a single DFT spread OFDM symbol, hereinafter referred to as OFDM symbol, due to a characteristic of the DFT spread OFDM system.
In LTE-Advanced, fundamental communication services need to be provided in a higher frequency spectrum and at a higher mobile velocity than those of LTE. However, a reference symbol structure based on an LTE system has difficulty in satisfying this. In LTE-Advanced, an environment with higher Doppler spread is formed when compared to an environment based on the LTE system. Therefore, it is difficult to expect a satisfactory performance with the reference symbol structure in the LTE system.
To solve the aforementioned problem, the frequency of reference symbols per slot may be increased in a time axis. To increase reference symbols in the time axis, the number of OFDM symbols which transmit reference symbols per slot may be increased. However, while an improvement in a performance of the channel estimation is ensured, an overhead increase due to the reference symbols may lead to a decrease in a data transmission rate.
As another scheme for solving the aforementioned problem, a reference symbol and data may be multiplexed in a single OFDM symbol, and transmitted. Then, the proportion of the reference symbols in a single OFDM symbol may be decreased. Accordingly, while the overhead due to the reference symbols per slot remains constant, a temporal frequency of reference signals per slot may be increased. To multiplex data and a reference symbol in a single OFDM symbol, methods of time division multiplexing (TDM), frequency division multiplexing (FDM), code division multiplexing (CDM), and the like may be considered. As a TDM method, a method of multiplexing data and a reference symbol in a time domain prior to a DFT in a sequence of generating a DFT spread OFDM signal may be considered. In this case, an overhead due to a cyclic prefix may increase, interference between data and a reference symbol in a data reception apparatus may increase, and the channel estimation may be complex.
In a CDM method, an increase in the cyclic prefix, interference between data and a reference symbol, and the like may occur at the same time.
The present invention discloses a multiplexing structure of data and a reference symbol having an interleaved FDM (IFDM) structure in which data and a reference symbol are mixed by an FDM.